1. Field of the Invention
The present invention generally relates to an ink transfer arrangement for and method of transferring ink to an etched or engraved die or plate surface of a movable die or plate in a printing press, especially an intaglio or engraving press for producing engraved documents, such as securities or stationery, and, more particularly, to the transfer of differently colored inks in close proximity to each other during each inking of the die or plate surface.
2. Description of the Related Art
Intaglio printing on paper from an engraved plate was originally performed by a manually operated plate press. Thereupon, motor driven die stamping and embossing presses were developed for faster printing. Typically, an ink transfer arrangement in the motor driven press included an ink fountain pan for containing a supply of ink, a fountain roller partially immersed in the ink, and a transfer roller for picking up ink from the fountain roller and depositing the picked-up ink over the engraved or etched die or plate surface to be inked. The deposited ink is then wiped off the die or plate surface, leaving ink in the lines or grooves etched or engraved below the die or plate surface. The so treated surface is then pressed against sheet material such as paper to produce an engraved document. Reference can be had to U.S. Pat. No. 4,669,379 for details of an intaglio printing press.
Typically, an ink fountain pan contains ink of a single color. When multicolored engraved documents are desired, it is common to perform multiple passes of the paper through the press, each pass being made with a differently colored ink, thereby requiring perfect registration and positioning of each colored ink, in its turn, during separate ink transfer operations. Such separate operations limit the maximum production speed. Faster printing speeds were a primary consideration in the development of thermography.
Ink fountain pans having multiple differently colored ink supplies have been proposed. However, the differently colored inks were separated well apart, on the order of xc2xe of an inch, in order to prevent the inks from mixing and contaminating each other. Such large separations, however, were impractical where differently colored engravings were required to be positioned close together, for example, on the same line, or where the document was relatively small, for example, a business card.
Accordingly, it is a general object of this invention to transfer differently colored inks in close proximity to each other over an etched or engraved die or plate surface.
More particularly, it is an object of the present invention to increase the maximum printing speeds of die presses for producing multicolored engravings.
Still another object of the present invention is to control the spacing between differently colored inks deposited over a die or plate surface.
In keeping with the above objects and others which will become apparent hereafter, one feature of the present invention resides, briefly stated, in an ink transfer arrangement for, and method of, transferring differently colored inks to an etched or engraved work surface of a movable die or plate in a printing press. The invention includes an ink fountain pan mounted on the press. At least one partition divides the fountain into a plurality of compartments each containing a differently colored ink.
A rotatable fountain roller is mounted on the press for rotation about a fountain axis. The fountain roller has a plurality of cylindrical fountain roller portions corresponding in number to the plurality of compartments. Each fountain roller portion has at least a portion of its outer circumferential surface in inking communication with the differently colored ink in a respective compartment. Two of the fountain roller portions are spaced apart along the fountain axis by a spacing or annular channel in which said at least one partition is received.
The invention further includes means for rotating the fountain roller to distribute the differently colored inks in adjacent relation axially separated by said spacing circumferentially along the outer circumferential surfaces of the respective fountain roller portions during rotation of the fountain roller. A rotatable transfer roller is mounted on the press for movement between a pick-up position in which the transfer roller is in inking engagement with, and rotated about a transfer axis by, the fountain roller to transfer the differently colored inks at said spacing along an outer circumferential surface of the transfer roller during rotation thereof, and an inking position in which the transfer roller laden with the differently colored inks is in inking engagement with the work surface to apply the differently colored inks thereto during movement of the die.
In further accordance with this invention, means are provided for moving the transfer roller between the pick-up and inking positions, and for pressing the transfer roller against the work surface with a pressure sufficient to cause the differently colored inks to flow in opposite directions along the transfer axis towards each other to apply the differently colored inks to the work surface at a distance smaller than said spacing.
Thus, differently colored inks can be applied to the work surface in a single movement of the transfer roller and at a closer spacing than heretofore. In the preferred embodiment, the axial spacing on the fountain and transfer rollers is less than 0.10 inches and is, preferably, 0.060 inches. The distance between the inks on the work surface can be made to be just touching or xe2x80x9ceffectively zeroxe2x80x9d. This feature enables multicolor engravings on a single printed line, or series of lines.
The partition is preferably constituted of a material different from that of the fountain roller. The partition material is polyurethane, polypropylene, Teflon(trademark), or like plastic material, or is a metal such as bronze. The partition is snugly received in the spacing and preferably is in sliding, wiping contact with the fountain roller portions.
The transfer roller has a resilient material at its outer circumferential surface. Preferably, the transfer roller is constituted of rubber when solvent-based inks are used, and of polyurethane when water-based inks are used. The resilient material yields when pressed against the engraved die surface in the inking position.
A plurality of partitions can be used to divide the fountain pan into the compartments. In some applications, up to six different inks and compartments are utilized. There is no cross contamination of differently colored inks due to the partitions.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.